Definition

1.

"[A]n open-source electronics prototyping platform based on flexible, easy-to-
use hardware and software. It’s intended for artists, designers, hobbyists, and
anyone interested in creating interactive objects or environments . . . It’s an
open-source physical computing platform based on a simple microcontroller
board, and a development environment for writing software for the board."
(http://www.arduino.cc/)

2. What is Arduino?

"Arduino is a tool for making computers that can sense and control more of the physical world than your desktop computer. It's an open-source physical computing platform based on a simple microcontroller board, and a development environment for writing software for the board.

Arduino can be used to develop interactive objects, taking inputs from a variety of switches or sensors, and controlling a variety of lights, motors, and other physical outputs. Arduino projects can be stand-alone, or they can be communicate with software running on your computer (e.g. Flash, Processing, MaxMSP.) The boards can be assembled by hand or purchased preassembled; the open-source IDE can be downloaded for free.

The Arduino programming language is an implementation of Wiring, a similar physical computing platform, which is based on the Processing multimedia programming environment."
(http://www.arduino.cc/en/Guide/Introduction)

3. S. De Paoli and C. Storni:

"Arduino is therefore a hardware and software platform whose goal is to
enable people to create interactive products or environments through the use
of electronic material that is widely available, inexpensive, and quite easy to
use. Essentially the board is composed of: (1) a series of digital and analog
ports for inputs (inputs can come from a variety of switches or sensors like
motion, light, proximity sensors, etc.); (2) a series of output ports connected
with whatever actuator is used (motor, lights, computerized devices); and (3) a
central processor (a microcontroller chip) with a flash memory where the user
writes and flashes specific instructions (via USB) on how to process inputs
into outputs (figure 2). The Source Code for controlling the board is written
by using a specific FOSS programming language called ‘‘Processing’’
(http://p2pfoundation.net/Sociotechnical_Skills_in_the_Case_of_Arduino)

Description

1.

"Arduino is an open-source electronics prototyping platform based on flexible, easy-to-use hardware and software. It's intended for artists, designers, hobbyists, and anyone interested in creating interactive objects or environments.

Arduino can sense the environment by receiving input from a variety of sensors and can affect its surroundings by controlling lights, motors, and other actuators.

The microcontroller on the board is programmed using the Arduino programming language (based on Wiring) and the Arduino development environment (based on Processing). Arduino projects can be stand-alone or they can communicate with software on running on a computer (e.g. Flash, Processing, MaxMSP)."

2.

"At its heart, Arduino is a programmable microcontroller, which was developed in Italy in 2005. You can connect the microcontroller via a serial or USB connection to a computer running Windows, Mac OS or Linux, and program it using the free open-source integrated development environment.

Arduino is often described as a physical computing platform because you can use sensors to measure motion, light or temperature, and to flash LEDs or lights, sound buzzers or run motors. Arduino also has communications extensions that add Bluetooth, Ethernet or wireless-mesh networking capabilities, and can be triggered by events on the web or via web APIs.

During the Guardian's recent hack day, Arduino was used to create a robot that responded to hashtags on Twitter. It powered a device to alert journalists when people were reading their stories, and the team from Arduino consultancy Tinker.it built a leaderboard that measured responses to the Twitter accounts of the main British political parties.

Alexandra Deschamps-Sonsino, CEO of Tinker.it, says all kinds of people are using the platform, including hobbyists and engineers but also artists and designers – people who don't have a technical background. Clothing designers even use Arduino with special circuit boards that can easily be sewn into fabric.

You can buy pre-built Arduino boards or, true to the open-source movement, can download plans and build your own. To rapidly create prototype projects many Arduino enthusiasts use solder-less breadboards. To get started Deschamps-Sonsino suggests going to the "playground" on the Arduino website. It has a list of projects broken down by difficulty and purpose. For instance, there are audio, visual, and communication projects, as well as physical or mechanical projects.

From a detailed reportage on the place of Arduino in the Italian tradition of interaction design, by Nathan Waddington and Russell Taylor:

"The Arduino platform is fast becoming a platform of choice for
interaction designers, and open source is a big part of that choice, even if it
is an unintentional (or unknown) part of that choice. Open source allows for
effective iterative design and creates a community out of the users. Physical
computing specifically is not interaction design, but it is becoming more and
more an integrated part of interaction design. During the summer of 2007,
the Italy Design SFU Field School went to Italy and interviewed several top
Italian designers. Among them was Massimo Banzi, an interaction designer
who helped to design the Arduino. He took the time to tour the field school
participants through the manufacturing process, the factory where the
boards are made and assembled, gave a lecture on his previous (and current)
works and finally, agreed to be interviewed for the project. Much of this
paper derives from those tours and interviews. It is clear that around Massimo
a community of young designers is growing, working in ways unfamiliar in
Italy. This is yet another place where we see new growth in Italian Design.

So, what is Arduino? The Arduino is a tool. A little computer that
can help designers interact with the physical world. Ostensibly though, it’s
not much more than any other similar platform; what makes it special is how
it’s been designed and supported. “Arduino is an open-source electronics
prototyping platform based on flexible, easy-to-use hardware and software.

It’s intended for artists, designers, hobbyists, and anyone interested in
creating interactive objects or environments” (Arduino, 2007). The key is its
intention – intended for artists and designers, two groups of people whose
backgrounds aren’t necessarily technical ones (or if they are, they aren’t likely
to be deep in embedded computing). So, in the city where Olivetti once
stood (it is now a part of Telecom Italia), the designers of Arduino substituted
corporate ownership and support with community and openness. This shift
is what makes the Arduino accessible, and it is what has caused its rapid
growth and popularity in the communities using it. So why was it developed?

“Physical computing is about creating a conversation between
the physical world and the virtual world of the computer” (O’Sullivan &
Igoe, 2004, pp xix). The Arduino was developed initially to help students
at Interaction Design Institute Ivrea to develop projects of their own. The
students needed a platform to build their interactive projects on which would
ease the burden of entering into the physical computing realm. Students with
limited computing knowledge could program working prototypes themselves
and take radical ideas developed in the hothouse of a good design school
into stuff that actually worked and could be used and played with by an
audience. Traditionally physical computing has been the domain of computer
science students, professional programmers and hardware developers who
use other kinds of basic hardware (such as a basic stamp, a kind of hardware
platform with basic components sufficient to run an application, CPU,
memory, etc.) to deal with sensor input and output to devices. However, now
the barriers to entry have been significantly reduced with the Arduino, as the
hardware is very cheap and readily available and the software is much more
forgiving and user-friendly than that of other hardwares. Using Arduino,
students can get up and running quite a bit faster than they otherwise could.

And for many that becomes addictive and professionally valuable. The Ivrea
students for instance have had great success getting work at Interaction
Design stalwarts such as IDEO London. And of course, all these people using
the boards has fed back into the production process for improving the boards
through the company’s open source development."
(http://www.sfu.ca/italiadesign/2007/page/papers/arduino-and-open-source-design.pdf)

Details and FAQ

Excerpts from the FAQ:

How can I get an Arduino board?

You can buy an Arduino board from one of the distributors listed on the buy page. If you'd prefer to build your own, see the Arduino Single-Sided Serial board, which can be easily etched and assembled.

Who makes Arduino boards?

Most of the official Arduino boards are manufactured by SmartProjects in Italy. The Arduino Pro, Pro Mini, and LilyPad are manufactured by SparkFun Electronics (a US company). The Arduino Nano is manufactured by Gravitech (also a US company).

Which are the official Arduino boards?

The official Arduino boards are the ones listed on the hardware page: the Uno, Mega2560, Nano, Bluetooth (BT), LilyPad, Mini, Pro, Pro Mini, and a few older models, along with the Ethernet, XBee, motor, and prototyping shields. These are boards whose manufacturers work with the Arduino team to ensure a good user experience, compatibility with the Arduino software, and a quality product. In return for their status as official boards, the manufacturers pay a licensing fee to the Arduino team to support the further development of the project.

In general, we try to restrict use of the name "Arduino" to the official boards. If you find a product under a different name but described as "Arduino compatible", itâ€™s probably not an official board and doesnâ€™t fund continued work on the project."
(http://arduino.cc/en/Main/FAQ)

License

Stefano De Paolia; Cristiano Storni:

"The board schematics and design files are released under the ‘‘Attribution
share alike 3.0’’ Creative Commons’ (2010) license (http://creativecommons.
org/licenses/by-sa/3.0/). In this way, anyone can produce copies of the board,
redesign it, or even sell boards that copy the design. Under the provisions of
this license, one does not need to pay a fee to the Arduino team or even ask
their permission. However, anyone republishing the reference design, has to
credit the original Arduino group (this is the ‘‘Attribution’’ part of the
license). Moreover, if someone tweaks or changes the board, the new design
must use the same or a similar Creative Commons license to ensure that new
versions of the board’s schematic will be equally without fees and open to
future modification and redesign. In this case, the mentioned language used
to program the microcontroller (Processing) is a FOSS language readapted by
the Arduino team to deal with microcontroller-enabled tangible computing."
(http://p2pfoundation.net/Sociotechnical_Skills_in_the_Case_of_Arduino)

The Arduino Trademark

Stefano De Paolia; Cristiano Storni:

"The only thing that is outside
the direct control of users is the name Arduino, which is a registered
trademark.

Indeed, there is a specific strategy in place here, as an interviewee
pointed out:

- The only protection we have in play regards the name of the board that is
trademarked. If you want to make a board and called it Gino, it is ok with me
and I do not care. But if you make a board and you called it Arduino you
cannot. We want to prevent the diffusion of low quality copies. Arduino for us
means that the design respects certain quality as the ease of use, the quality of
the components and of their assemblage.

Arduino integrated development environment

Stefano De Paolia; Cristiano Storni:

"The ‘‘Arduino integrated development environment’’ is a software (where
one edits the Processing language) released under GNU General Public
License (GPL), and it is used to write and flash the code into the board’s
memory. The GPL embodies a Copyleft clause that gives the user the rights to
change and distribute the software, provided that new enhancements are
released under the same license (Stallman 2002). Finally, the Arduino web
site, where a collection of libraries of code examples from the user community
grows on a daily basis, has also been released under Creative Commons so
that people can freely make use of all the scripts, code, and tricks posted by
users. This makes the appropriation of Arduino even easier because
inexperienced users can take advantage of solutions and tutorials prepared
by peer users who share their expertise online. The only thing that is outside
the direct control of users is the name Arduino, which is a registered
trademark."
(http://p2pfoundation.net/Sociotechnical_Skills_in_the_Case_of_Arduino)

The Arduino Enterpreneurial Coalition

"Several quirky companies have also emerged. For example, a firm called
Botanicals has developed an Arduino powered device that monitors house-
plants: this phones (or tweets) when the plant needs to be watered. The web
site Makezine.com inaugurated an Arduino section by introducing the board
as the best all around centerpiece to a modern electronics project, and listing
a huge series of step-by-step tutorials on how to build Arduino-powered
gadgets. Also Ponoko.com*one of the biggest DIY technology web sites*
sells Arduino-based products along with a series of add-ons that extend the
possibility of the board. "
(http://p2pfoundation.net/Sociotechnical_Skills_in_the_Case_of_Arduino)

History

1. Stefano De Paolia; Cristiano Storni:

"The Arduino was initially designed for teaching purposes in a well-known
design institute in Italy.

As one of the main three original developers of the
board recalled in an interview:

- We already worked with Processing a lot. At that time Processing was limited to
graphical animation. Basically students used it to do graphics. When dealing
with tangible and real-time interaction we had to use another language. One
day we asked ourselves: why not use Processing to generate programs for our
hardware too? (Arduino Developer, Interview October 2008)

Initially, a hardware-specific programming language was used with another
board, one more expensive and less open than the actual Arduino. The idea
soon emerged of developing an agile, easy-to-use and open board, with an
integrated development environment. A specific module for the Processing
language was consequently implemented by the original developers so that
students would not have to learn another language in order to program
hardware in their tangible computing prototypes. A couple of months later,
the first Arduino Board was ready, paid out of the developers’ own pockets.
Along with it, a first series of demonstration workshops was arranged by the
three developers, where the boards were provided to students and teachers.

Interviewees recall a big design workshop in Madrid in 2005, followed by one
in London and then in Copenhagen. Many Arduino boards were given away
for free to teachers who wanted to explore the possibility of adopting the
Arduino for their classrooms. In a few months, the Arduino board gained
widespread popularity in design institutes all over Europe and*due to word-
of-mouth*within many ‘‘Do It Yourself’’ communities.

In this OH project the role of users*in terms of inscribed affordances and
constraints*is only partially defined by the developers. The Arduino board is
intended to be the central core for the implementation and prototyping of
interactive products or environments designed by the users themselves. In this
sense, the design possibilities and the different ways of appropriation for users
are endless, also because Arduino developers*in their strategy*have
inscribed quite weak forms of control over future uses. The board design
does not anticipate the negotiation of its role as would happen in proprietary
software. Instead, it remains equally open through a series of inscriptions that
sustain a specific strategy."
(http://p2pfoundation.net/Sociotechnical_Skills_in_the_Case_of_Arduino)

2. Alicia Gibb:

"The Arduino microcontroller is a principle representative of the microcontrollers
commonly used in art and design. Others in the field include Wiring, Making Things, PIC, and the Basic Stamp.

The Arduino microcontroller was originally created as an
educational platform for a class project at the Interaction Design Institute Ivrea in
2005. It grew from the previous work of the Wiring microcontroller designed by
Hernando Barragán in 2004.

From its inception, the Arduino was developed to engage
artistic and design-oriented minds.

Barragán, an artist and designer, created the Wiring microcontroller to be used
as a tool for a parsing data to electronics. He intended it to be used by a “non-technical”
audience: “artists, designers, and architects,” in short, not requiring prior electrical
engineering or computer science knowledge. He emphasized the Wiring board as a
prototyping tool. Wiring fulfilled Barragán‟s need for a designer-friendly tool (in this
case a microcontroller) that was easy to use without a great deal of engineering or
programming experience. Barragán‟s advisors for his thesis on Wiring were Casey Reas
and Massimo Banzi. Reas created the visual programming language Processing with
Ben Fry. Reas studied interaction in art as an undergrad,
continued with John Maeda
while at MIT, and developed Processing for a language accessible to artists and
designers. Banzi, on the other hand was more interested in further developing the
microcontroller as an art and design tool. The Arduino was originally developed
for an interaction design class taught by Banzi. The creators of the Arduino are Massimo
Banzi, David Cuartielles, Dave Mellis,26 Gianluca Martino with Nicholas Zambetti.

The Arduino team currently consists of Banzi, Cuartielles, Martino, Mellis and Tom Igoe.

The Arduino team wanted to further simplify the Wiring platform and thus the
Arduino microcontroller was developed. The Arduino team made the Arduino
microcontroller more usable by focusing on simplicity, a goal in pursuit of designing for
a non-technical audience. Four cohesive reasons are echoed by Banzi when defining the
Arduino‟s success.

These reasons also denote Arduino‟s differences from other
similarly intended microcontrollers for artists and designers:

1. It is inexpensive

2. It is packaged with the Integrated Development Environment (IDE).

3. It is programmable via USB.

4. It is supported by a community.

The above points were deliberate decisions when the Arduino platform was being
conceptualized and designed. The usability of the Arduino platform is significant being
that every person interviewed spoke directly of the usability of the Arduino. Three people
interviewed currently work at IDEO, and are experts in the field of usability. Participants
were asked how they would describe the level of entry to the Arduino versus other
microcontrollers. The answer was unanimous that the Arduino was easier to use. From
having a simplified platform with a chip on board to a user-friendly Integrated
Development Environment (IDE), made a difference to new users and people who
appreciate visual aesthetics. Mellis comments that their goal was to make it less
expensive and smaller than the Wiring board, “A lot of things people tend to build
initially tend to be simple, they don‟t need a powerful microcontroller”. Ninety-Four
percent of interviewees felt the four points outlined by Banzi; cost, an integrated IDE,
programmable over USB, and supported by a community, were useful in their work and
made the Arduino a successful platform."
([1])

Status

Technical

"The Arduino prototyping platform is a good example of all this. It can be programmed to read sensors, control motors and build interactive objects and artistic installations. Its compiling environment is multiplatform and free (as in freedom) and the only extra hardware needed for programming it is a serial/ USB cable. This software can be downloaded from the website Arduino web site, which also contains Arduino schematics released under Creative Commons Attibution-ShareAlike. The project has used many ingredients to achieve a successful widely used project. For example, it contains a removable Atmega8 microcontroller which can be easily replaced if broken—without the need to buy a new Arduino board. Two years after its creation, you can see an expanding community of developers who support it, workshops all around the world, new plugins and modules like ArduinoXbee (ZigBee communications interface), Arduino BT (arduino with bluetooth connectivity), Arduino Mini or the recent Arduino GPS, and third party projects as SquidBee."
(http://www.freesoftwaremagazine.com/articles/making_open_hardware_possible)

Market Penetration

Regarding Google choosing the open source hardware platform (Arduino) for the “Android Open Accessory” kit, by Phillip Torrone, May 12, 2011:

"Besides there being about 300,000+ Arduino “in the wild,” I estimate there are about half a million people somehow doing something with the Arduino, from students to people not even realizing they’re using this open platform in some way (Processing, education, etc). For a microcontroller platform, as I’ve said before, it’s won and it’s here to stay. Community, open IDE, open hardware, no-mess drivers, cross platform — it’s fairly cheap and easy to get going and do something right away. There really isn’t an easier way to get analog sensor data or control a motor easier and faster than with an Arduino — and that’s a biggie, especially if you’re a phone and want to do this.

So with millions of phones out there and Google looking to make it dead simple to develop accessories, what easy-to-use, sensor-ready, open source platform has enough umpf to get this party started? Arduino. I’m sure that’s debatable (head to comments), but really, what else would be a better match?

Discussion 1

Is Arduino Open Source?

"Yes. The source code for the Java environment is released under the GPL, the C/C++ microcontroller libraries under the LGPL, and the schematics and CAD files under Creative Commons Attribution Share- Alike licenses. I want to design my own board; what should I do? The reference designs for the Arduino boards are available from the hardware page. They’re licensed under a Creative Commons Attribution Share-Alike license, so you are free to use and adapt them for your own needs without asking permission or paying a fee. If you’re looking to make something of interest to the community, we’d encourage you to discuss your ideas on the hardware development forum so that potential users can offer suggestions. What should I call my boards? If you’re making your own board, come up with your own name! This will allow people identify you with your products and help you to build a brand. Be creative: try to suggest what people might use the board for, or emphasize the form factor, or just pick a random word that sounds cool. \”Arduino\” is a trademark of Arduino team and should not be used for unofficial variants. If you’re interested in having your design included in the official Arduino product line, please see the So you want to make an Arduino document and contact the Arduino team. Note that while we don’t attempt to restrict uses of the \”duino\” suffix, its use causes the Italians on the team to cringe (apparently it sounds terrible); you might want to avoid it."
(http://www.adafruit.com/blog/2009/03/28/open-source-hardware-overview-slides/)

What do you mean by open-source hardware?

"Open-source hardware shares much of the principles and approach of free and open-source software. In particular, we believe that people should be able to study our hardware to understand how it works, make changes to it, and share those changes. To facilitate this, we release all of the original design files (Eagle CAD) for the Arduino hardware. These files are licensed under a Creative Commons Attribution Share-Alike license, which allows for both personal and commercial derivative works, as long as they credit Arduino and release their designs under the same license.

The Arduino software is also open-source. The source code for the Java environment is released under the GPL and the C/C++ microcontroller libraries are under the LGPL."
(http://arduino.cc/en/Main/FAQ)

Five Reasons why Arduino is popular

Wired:

(By Priya Ganapati, July 6, 2010)

Here are five reasons why the Arduino is more popular than the BeagleBoard:

Starter Projects

Editing and rewriting is often easier than writing from scratch. It’s the same with electronics. It’s easier to mod an idea than start with a blank slate.

That’s where the BeagleBoard falls short. “It has virtually no example application that you can just copy and hack to learn from,” says Massimo Banzi, one of the co-founders of the Arduino project.

The Arduino has hundreds of projects and ideas that are cooked up and shared by its users. For instance, check out this list of 40 Arduino projects that includes ideas such as a Wiimote-controlled Espresso machine, a biking jacket that flashes a turn signal and a wireless electricity monitor that tweets your power usage.

It’s a chicken-and-egg problem for the BeagleBoard. Unless there are more example codes out there, it is difficult to draw in the audience. And without the audience it is challenging to get enough sample projects into the community.

Cost and Durability

At $30 a piece, an Arduino is an inexpensive investment for someone who wants to try it out. “It’s the price of a few sandwiches,” says Torrone.

Compare that to the BeagleBoard-xM, which costs $180.

One reason why the Arduino is so cheap is because it is easy to clone. The microcontroller is completely open source so the “components are all commodity,” says Torrone.

With the BeagleBoard, hobbyists don’t have the same amount of freedom. They have to work closely with Texas Instruments or its partners, says Torrone.

Arduino is also very resilient. Drop it, smash it and it still stays alive. Add to that its low-power requirement, and the product becomes a must-have for DIYers. An Arduino can run on a 9V-battery for days.

“The BeagleBoard is fast and powerful but that also means lots of energy is needed, which makes it difficult for simple projects,” says Torrone.

A Thriving Community

Arduino’s popularity means it’s easy to get started. Companies such as Adafruit, SparkFun and Liquidware not only sell chips, but they also host blogs that suggest ideas on how to use your Arduino while providing extensive project plans to guide you in completing your creations.

Will Chellman, a student who has played with Arduino for years, says he’s now experimenting with the BeagleBoard. But finding documentation and information to work off is not easy, he says.

The lack of well-documented projects done with the BeagleBoard can be intimidating to new users as well, says Banzi.

“There’s lots of of interesting stuff (about the BeagleBoard) but it is very technical,” he wrote in a comment recently on Gadget Lab in response to the launch of BeagleBoard-xM.

Banzi says BeagleBoard documentation is also scattered and fragmented.

“Parts of it have aged and you spend quite a bit of time jumping from wikis to mailing list to track which specific bit of documentation applies to your board, bootloader etc.,” he says.

Maturity Is the Key

Arduino has had a head start on the BeagleBoard. By October 2008, about 50,000 Arduino boards had already been shipped. That year, the first BeagleBoards started making their way into the hands of hardware enthusiasts.

“The BeagleBoard is just two years old. Since it hasn’t been around long enough, there’s not enough people building apps based on it,” says Chellman.

That’s not to say that BeagleBoard isn’t catching up. Earlier this month, we showed five projects ranging from a videowall to the iPad of ham radios that use the BeagleBoard. There’s also a build-your-own tablet kit that is based off the BeagleBoard.

If DIYers take a shine to it, expect to see more ideas like these.

Simple Is Attractive

With its single-board computer configuration, 1-GHz processing power and the choice of accessories, the BeagleBoard is a creative engineer’s dream come true.

But the same reasons make it intimidating to those who want to geek out on a DIY project but don’t have the technical know-how.

Arduino users point out that it is simple to connect external sensors to the board, and the example codes out there make it easy to get started quickly.

Arduino is a simple system designed for creative people with little or “no prior knowledge of electronics,” says Banzi. “It’s cheap and open source with lots of documentation written in a not too technical language. Above all, it has a very welcoming attitude towards beginners and tries not to scare them too much.”
(http://www.wired.com/gadgetlab/2010/07/hardware-hobbyists-arduino/)

Why Arduino Won

By Phillip Torrone:

"The IDE Runs on Macs, Linux, and Win

The IDE works on a Mac, Win, and Linux, and it’s completely open source. The IDE is how you program the Arduino — it’s based on Processing (a graphics programming language and development system popular with artists and designers), which has been around for a long time. It runs on Macs and Linux, not just Windows, and that matters if you want to be inclusive. It’s based on a strong and well-supported backend, the open source gcc toolchain, and wrapped in Java, so porting is easy and bugs can be found and fixed. There are enough smart people using and working on the IDE to keep it going strong. Want freaky cool people to do neat stuff with your platform? You gotta have your IDE run seamlessly on a Mac and also Linux.

The Driver Actually Work On Macs, Linux, and Win

Again, like the IDE, the drivers to use the board work on Mac, Win, Linux, and the FTDI drivers “just work.” Sticking with serial, a well understood (but slow) interface, was a good call. Sure HID or something custom is cool and all, and can be much faster, but the serial chip works, can be used for debugging as well as programming, and easily slots into software tools like Java, Python, Perl, C, NET, BASIC, Delphi, MAX/MSP, and PureData, Processing, etc.

Libraries, Easy-to-Do Simple Things, Easy-to-Do Hard Things

There are tons of object-wrapped libraries to do complex things, like writing to SD cards, LCD screens, parsing GPS. And there’s are also libraries to do simple things, like twiddle pins or debounce buttons. We’ve written UART setup code 10 times for 10 chips and frankly, we’re tired of it. Much nicer to just call Serial.begin(9600) and have it sort out the registers for us.

Lightwight, Runs on the Metal

The code runs directly on bare metal, with a well-tested and understood compiler (we would even say that avr-gcc is the default/standard compiler for AVR.) It’s not interpreted like .NET or BASIC. It’s fast, it’s small, it’s lightweight, and you can use the HEX file to program fresh chips in bulk.

Sensors

The Arduino really took off because it has analog-to-digital input, in other words, you can take in sensor data like light, temperature, sound, or whatever using the low-cost sensors already on the market and get that into the Arduino easily. It also has ready-to-go SPI and I2C for digital sensors. This covers 99% of sensors on the market. You can’t easily do this with other platforms — it’s completely bizarre to see a BeagleBoard (great product) with an Arduino basically strapped to it just to get sensor data in.

Simple, But Not Too Simple

Many dev boards are historically enormously complex with a lot of added-on parts like LCDs, buttons, LEDs, 7-segments, etc,. showing everything it can do. Arduino has the bare minimum. Want more? Get a shield. There are hundreds of Arduino shields, from LCD to Wi-Fi, but it’s up to the user to add that. Shields add extra functionality easily, and there is a business incentive for others to make them.

Not Made By a Chip Maker

The board was not designed by a chip maker. Why is this important? Chip makers often want to show how their product is different so they add weird things to differentiate themselves. The Arduino highlights commonalities between microcontrollers, not the differences. This means that the Arduino is a perfect beginner platform – everything you can do with an Arduino you can do with any other microcontroller, and the basics will last you for a long time.

Low Cost

You can get an Arduino for $30, and we’ll probably see $20 Arduinos soon. Many dev boards start at $50 and could easily get to $100+, although now we’re seeing chip companies start to realize that its worthwhile to have a more pragmatic pricing strategy.

Open Source

While it’s nice that Arduino is open source, and commercial use is allowed if you make a clone, it’s not the biggest reason, which is why it’s down near the end of the list. However, that isn’t to say it doesn’t matter at all. Specialized derivatives can be made without paying someone or asking anyone. It’s open source hardware so a company or school can use it without any per-seat licensing. There’s no risk that it will be discontinued and the software gone forever. If you want a new feature, you can spend the time and get it added. When thousands of people have a small stake in something, or ownership, they care more. Does anyone even debate if open source software is a good idea any more?"
(http://blog.makezine.com/archive/2011/02/why-the-arduino-won-and-why-its-here-to-stay.html)